1. Field of the Invention
The present invention relates to a vehicle air conditioner with a hot-gas heater cycle in which an interior heat exchanger is operated as a radiator by introducing hot gas refrigerant from a compressor directly into the interior heat exchanger. More particularly, the present invention relates to an accumulator having a heating device for heating refrigerant in the accumulator of the hot-gas heater cycle of the vehicle air conditioner.
2. Description of Related Art
A conventional vehicle air conditioner, disclosed in JP-A-11-42934, performs heating operation using a hot-gas heater cycle in a refrigerant cycle system. In this conventional vehicle air conditioner, when a temperature of cooling water (hot water) from the vehicle engine to a heater core is lower than a predetermined temperature, for example, when operation of the vehicle engine is started, gas refrigerant discharged from a compressor is introduced directly into an interior heat exchanger while bypassing a condenser. In this case, heat is radiated from gas refrigerant to air in the interior heat exchanger, so that auxiliary heating function can be obtained from the interior heat exchanger. That is, in this conventional vehicle air conditioner, a single interior heat exchanger disposed in an air conditioning case is selectively operated as an evaporator in a cooling mode and as a radiator in a heating mode. Further, a heating device such as an electric heater is provided on a low-pressure refrigerant pipe for connecting the interior heat exchanger and a suction side of the compressor. Then, heating performance in the heating mode is improved by heating refrigerant in the low-pressure refrigerant pipe using the heating device. Specifically, pressure of refrigerant to be sucked into the compressor is increased by the heated low-pressure refrigerant, and a mass density of refrigerant to be sucked into the compressor is increased. Therefore, a flow amount of refrigerant is increased, and a compression work amount of the compressor is increased.
In the hot-gas heater cycle, an accumulator, for separating refrigerant into liquid refrigerant and gas refrigerant and for storing the liquid refrigerant therein, is provided in the low-pressure refrigerant pipe. Therefore, gas refrigerant balances with liquid refrigerant in the accumulator, so that low-pressure refrigerant becomes saturation gas refrigerant at an outlet of the interior heat exchanger. Thus, the heating device heats only the saturation gas refrigerant in the low-pressure refrigerant pipe. However, since a heat transmission rate of gas refrigerant is much smaller than that of liquid refrigerant, a heat transmission amount from the heating device to refrigerant is necessarily reduced. Accordingly, heating performance cannot be sufficiently improved in the heating mode.